Process for texturizing proteinaceous materials

ABSTRACT

A process for texturizing an aqueous slurry of proteinaceous materials comprises forming an aqueous slurry of the proteinaceous material with a texturizing agent, freezing the aqueous slurry, dehydrating the frozen slurry, and heat treating the dehydrated slurry at a temperature between about 80° to about 300° C. to set the structure. The resultant sponge-like texturized product absorbs water but will not disperse in water.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to texturization processes for proteinaceousmaterials.

2. Description of the Prior Art

Protein products are used in foods for their functionality as well astheir nutritional value. The texture of a protein product contributes toits functionality as well as to its taste. Most vegetable proteinproducts, e.g., soybean protein products, are in the form of powders orgrits and a texturization technology has been developed to incorporatesome textural characteristics to such soybean proteins. One knownprocess produces meat substitutes from edible protein materials byforming fibers or filaments and then binding the fibers by suitablemeans. In this process protein fibers are prepared from a spinning dopeof protein which is forced through a porous membrane such as a spinneretto form fibers. These fibers are coagulated in a bath containingsuitable acids and salts and are oriented by suitable means, such as bya series of rolls revolving at increasing speeds. The fibers are placedin a salt solution, such as sodium chloride, of sufficient concentrationto prevent the fibers from dissolving.

Textured protein foods can also be produced without spinning. Such aprocess involves rapid orientation and coagulation of protein materialin a substantially undenatured, finely-divided, hydrated state underconditions which produce a shred-like structure. Orientation andcoagulation of protein must be interrelated such that coagulationfollows orientation of the molecules, whereby upon coagulation theoriented molecules are set in a shred-like condition. The process isconducted with about a 50% slurry of the protein material in water. Theslurry is rapidly heated to and maintained at 360° F. for about 1 minutein an autoclave and cooled rapidly. A shredded meat-like texture isobtained.

In various other processes mixtures of proteins can be used where one ofthe proteins serves as a binder. In such mixtures gluten or egg white isgenerally used as a heat-coagulating ingredient to set the extruded orshredded protein textures.

In another process a chewy gel is prepared by (a) adjusting thecomposition of a protein-water system, in particular the pH and thesolids content, to a composition conducive to gel formation, (b) shapingof the system, and (c) applying heat as necessary to produce a chewygel. The shaping may take place before or after either of the othersteps of the process. The final products produced in accordance withthis process simulate the fibrous texture, chewiness and structure ofmeats such as pot roast, roast beef, or the like.

In another process a textured soybean meal product is produced bymoistening the soybean meal, mechanically working the moistened meal inan extruder at a temperature above 212° F., pressurizing the moistenedmeal sufficiently to create a flowable substance, and extruding thepressurized substance through an orifice into a zone of lower pressureto produce a textured product.

SUMMARY OF THE INVENTION

In one aspect, the invention resides in a process for texturizingproteinaceous materials comprising: forming an aqueous slurry of theproteinaceous material, said slurry including a texturizing agent;freezing the aqueous slurry; dehydrating the frozen slurry; and heattreating the dehydrated slurry at a temperature of from about 80° toabout 300° C. to yield a water-stable textured product. The texturizingagent is selected from the group consisting of protein isolates, proteinconcentrates, gelatin, or mixtures thereof. Soy isolate is a preferredtexturizing agent. The proteinaceous materials can be plant proteinmaterials such as soybean proteins, cottonseed proteins, etc., animalproteins such as fish proteins, milk proteins, meat proteins, etc., orthey can be microbial protein materials such as yeasts. In this regard,preferred yeasts are Candida utilis, Saccharomyces cerevisiae,Saccharomyces fragilis, and Saccharomyces carlsbergensis because oftheir approval by the Food and Drug Administration. The process isapplicable to all microbial cells, however.

The frozen slurry can be dehydrated in several ways including freezedrying, oven drying, microwave oven drying, and soaking the frozenslurry in an alcohol at a temperature at or below that of the frozenslurry. In the latter case, the water molecules diffuse out of thefrozen structure and are replaced by the cold alcohol. It has beendiscovered that alcohol will not disperse the frozen structure, whereascontact with water without a prior heat treatment will cause thestructure to disperse. Oven drying can be accomplished at any suitabletemperature, preferably at from about 50° to about 200° C.

In addition, the dehydrated slurry must be heat treated to stabilize orcure the textured product to prevent dispersion when contacted withwater. It has been found that this can be conveniently done either bysimply placing the product in a dry air oven and heating, or it can beaccomplished by autoclaving the product in alcohol. The primaryobjective here is to heat the product to cure or set the structurewithout causing the structure to disperse, as will happen if it issoaked in water. Autoclaving is generally carried out at temperatures offrom about 120° C. to about 300° C., whereas oven treating is generallycarried out at from about 80° to about 250° C. Those skilled in the artwill appreciate that too high a temperature for too long a time willimpart a burnt taste to the product.

Optionally, the aqueous proteinaceous slurry can be heated at atemperature of from about 30° to about 130° C., preferably to about 70°C., and whipped to form a foam prior to being frozen. This additionalstep creates a more porous texture than would otherwise be obtainedwithout whipping. The heating step provides a degree of coagulation ofthe proteins to give the foam more body.

More specifically, the invention resides in a process for texturizing anaqueous slurry of single-cell protein materials such as yeastscomprising: adding to the slurry a texturizing agent selected from thegroup consisting of protein isolates, protein concentrates, gelatin, andmixtures thereof, the weight ratio of the single-cell protein materialsto the texturizing agent being in the range of from about 1:9 to about9:1; freezing the slurry; freeze drying the frozen slurry; and heattreating the dried slurry at a temperature of from about 100° to about250° C. to produce a textured product. The heat treatment can be carriedout by any suitable means such as heating in an oven or by autoclavingthe dried slurry in an alcohol such as ethanol at a temperature of fromabout 120° to about 300° C. and drying the autoclaved product.

In another aspect, the invention resides in a process for texturizing anaqueous slurry of single-cell protein materials comprising: adding tothe slurry a texturizing agent selected from the group consisting ofprotein isolates, protein concentrates, gelatin, or mixtures thereof;heating the aqueous slurry at a temperature of from about 30° to about130° C.; whipping the heated slurry for from about 1 to about 30 minutesto form a foam to preserve the foam structure; dehydrating the frozenfoam; and heat treating the dehydrated foam at a temperature of fromabout 130° to about 230° C. for from about 3 to about 120 minutes toyield a water-stable textured product. The resulting textured productcan be optionally further treated, for example by extracting withethanol to improve flavor. The frozen foam can be dehydrated by variousmeans, including oven drying at a temperature of from about 50° to about200° C., microwave drying, or freeze drying.

In a further aspect, the invention resides in a process for texturizingan aqueous slurry of single-cell protein materials comprising: mixingthe slurry with a texturizing agent selected from the group consistingof protein isolates, protein concentrates, gelatin, and mixturesthereof, the weight ratio of the protein materials to the texturizingagent being in the range of from about 1:9 to about 9:1; freezing themixture; soaking the frozen mixture in an alcohol having a temperatureat or below that of the frozen mixture to dehydrate the frozen mixtureby diffusing away the water molecules; autoclaving the frozen mixture inan alcohol at a temperature of from about 120° to about 300° C. for fromabout 3 minutes to about 90 minutes to make the product water stable;and drying the autoclaved mixture to yield a textured product.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following examples will serve to illustrate various aspects of thisinvention, without implied limitation. Examples 1-15 illustrate oneaspect of the process of this invention utilizing a heating and whippingstep prior to freezing the mixture.

EXAMPLE 1

Supro-7 (A protein isolate made from soybeans by Ralston Purina PurinaCo.) was suspended in water to obtain a 20 g./100 ml. water slurry. Thetemperature of the slurry was increased from ambient to about 70° C.gradually within about 15 minutes. During this time the slurry waswhipped to a consistency of beaten egg white. The whipped product waschilled to about 15° C. and the cold product was then frozen and freezedried. The dry product was microporous but was dispersible in water.When the dry product was heat treated at 200° C. in an oven for 12minutes, a light brown product resulted which did not disperse in waterand absorbed 22 times its weight in water. The wet product was flexiblelike a sponge and, when pressed, most of the water could be squeezed outwithout destroying the spongy texture. The wet product was chewy but wassticky. It had a fairly acceptable burnt taste.

EXAMPLE 2

A whipped product was prepared as in Example 1 except it was oven driedat 80° C. instead of freeze dried. The dry product was water dispersibleunless it was heat treated at 200° C. for 8-12 minutes. The heat curedproduct was brown in color. It became soft in water but it did notdisperse. The wet product had a bread-like porous texture whichpermitted water to be squeezed out of it without destroying the poroustexture.

EXAMPLE 3

A whipped product was prepared as in Example 1 except the whippedproduct was dried in a microwave oven instead of the freeze dryer. Thedry product was porous in texture. It dispersed in water unless heatcured at 200° C. for about 7-13 minutes. The heat cured product becamesoft and elastic when immersed in water and the water could be squeezedout of it by pressing without destroying the texture. The product waschewable and had a chewing gum-like mouthfeel.

EXAMPLE 4

Dried Torula yeast cells, grown on ethanol and extracted with ethanol,were mixed with Supro-7 (at 2 yeast/1 Supro-7 ratio) to obtain about 30g. dry weight/100 ml. water slurry. The temperature of slurry wasgradually increased from room temperature to about 85° C. within about25 minutes in order to facilitate the dispersion of Supro-7 while themixture was whipped to a whipped topping consistency. The whippedproduct was frozen at about 1/2 inch thickness and freeze dried. The dryproduct had a microporous texture but dispersed in water unless it wascured at about 200° C. for about 14 minutes. The heat cured product waslight brown in color. It surprisingly did not disperse in water andremained intact. The product had a sponge-like character and absorbedabout 18 times of its weight in water. The water could be squeezed outof it by pressing and could be reabsorbed when released. This operationcould be repeated a multiplicity of times without destroying thetextural characteristics of the product. Both the wet and the dryproducts were chewable and created a meat-like mouthfeel. No dispersionof single cells took place during chewing. The low moisture products hadan appearance of the ham and chicken meat analogues. The texturedproduct had a slight burnt taste.

EXAMPLE 5

A whipped product was prepared as in Example 4 except the frozen mixturewas dried in a microwave oven and then heat cured at 200° C. for about7-15 minutes. The product was light brown in color. It had a bread-likeor sponge-like porous texture and absorbed water easily. The water couldbe partially squeezed out by pressing, and this operation did notdestroy the texture of the product. The dry and wet products had apleasant meat-like mouthfeel and were chewable.

EXAMPLE 6

Example 4 was repeated, except that instead of freeze-drying, thewhipped product was oven dried at 80° C. and then heat cured in an ovenat 200° C. The resulting textured product had large and smallirregularly shaped pores and it absorbed water like a sponge. The wetproduct was elastic, chewable, and had a meat-like mouthfeel.

EXAMPLE 7

Twenty grams of ethanol-grown Torula yeast was mixed with 10 g. ofgelatin in 121 ml. water at room temperature. The temperature of themixture was increased to about 58° C. in about 7-10 minutes whilesimultaneously whipping the mixture using a kitchen mixer. The whippedmixture was cooled to about 15° C. The cold product had the feel of meatbut became liquefied when heated.

EXAMPLE 8

The whipped product obtained in Example 7 was frozen and freeze dried.The dry product dispersed in water unless heat cured at about 180° C.for about 10 minutes. The dry product was porous in texture and becamesponge-like in water. The wet product was elastic and the water could besqueezed out of it by pressing. The texture remained intact during thisoperation. The wet product developed a slightly meat-like flavor whenprepared by soaking the textured product in boiling water.

EXAMPLE 9

A textured product was prepared according to Example 4. The particlesize was reduced by grinding to about 5 mm. at the largest dimension.About 2.5 g. of these particles were wetted with about 4 ml. water andthe wet textured protein was mixed with about 47.5 g. lean ground beefand 1/4 teaspoonful salt. A hamburger pattie was prepared from themixture and cooked in a microwave oven for 1 minute. About 5 ml. ofjuice was released during cooking. About 4.5 ml. of the juice was fat.The mouthfeel of the cooked product was similar to hamburger, but itstaste was spicy. A control hamburger was prepared by using 50 g. leanground beef and 1/4 teaspoonful salt. Cooking in the microwave oven for1 minute released about 9.4 ml. juice, about 5.4 ml. of which was fat.As the hamburgers cooled down, the control hamburger became hard intexture, but the test hamburger remained relatively tender and juicy.

EXAMPLE 10

A textured protein product was prepared according to Example 4. The drytextured product was wetted with chicken broth. A product havingchicken-like texture and flavor was obtained.

EXAMPLE 11

Example 10 was repeated by using meat broth instead of chicken broth toobtain a meat-like tasting textured protein product.

EXAMPLE 12

The textured product obtained in Example 4 was extracted with about 70percent ethanol in water. A neutral tasting textured protein product wasobtained. The extraction did not harm the textural characteristics ofthe product.

EXAMPLE 13

The textured product obtained in Example 4 was extracted with water. Theextraction removed the burnt taste, reduced the brown color, andimproved the texture to closely resemble meat texture and mouthfeel.

EXAMPLE 14

A textured product was obtained according to the procedure outlined inExample 4, except the heat treatment was applied at 150° C. for 80minutes.

EXAMPLE 15

A textured protein product was prepared according to the procedureoutlined in Example 4, except the freeze dried product was heat treatedat 185° C. for from 10 to 30 minutes. The product was non-dispersible inwater and did not develop a brown color during the heat treatment unlessheated for a longer period than 30 minutes.

Examples 16-18 illustrate one aspect of the process of this inventionwherein the mixture is frozen, freeze dried, and heat treated.

EXAMPLE 16

Torula yeast (Candida utilis) was grown in a fermentor containing anethanol and minerals medium. The cells were harvested by centrifugationand the resulting paste (about 20 percent dry weight) was recovered. Thepaste was mixed with Supro-7 to obtain a yeast paste to Supro-7 ratio of2/1. Water was added to obtain slurries and pastes of about 10 percentto 30 percent dry weight at room temperature (about 23° C.). The aqueousmixtures were frozen over dry ice and freeze dried. The freeze driedproducts were white or light cream colored with a porous needle-liketexture. They dispersed in water unless they were heat cured in a hotair oven at about 175°-210° C. for about 30 to 10 minutes. The lowtemperature-treated samples were white to light tan colored while thehigh temperature-treated samples were light brown in color. When soakedin water, the heat treated samples absorbed water which could besqueezed out easily by pressing the product. Repeated application ofthis operation did not cause destruction of the textural characteristicsof the product. Both the dry and wetted products were chewable. Allsamples had a slight burnt taste which was heavier in highertemperature-cured samples. The burnt taste of the lowertemperature-cured samples was not objectionable.

EXAMPLE 17

Supro-7, ethanol extracted dry Torula yeast, and water were mixed at theratios indicated in Table I. The mixtures were frozen and freeze dried.The dry products were heat treated at 190° C. for 30 minutes and soakedin water. The water holding capacity of the products was determined andtheir textural characteristics were observed. The results are given inTable I.

                  TABLE I                                                         ______________________________________                                        Textural and Water Holding Characteristics of the Textured                    Products Prepared From Various Water Slurries                                                           Water                                                                         Holding                                                                       Index                                               Yeast   Supro-7  Water    (gH.sub.2 O/dry                                                                       Texture                                     (grams) (grams)  (ml.)    product)                                                                              in Water                                    ______________________________________                                        2       1         3       2       Tough meatlike                              2       1         6       4       Tough meatlike                              2       1         9         6.4   Medium soft                                                                   meatlike                                    2       1        12       7       Medium soft                                                                   meatlike                                    2       1        15       9       Soft meatlike                               2       1        18       9       Very soft                                                                     meatlike                                    ______________________________________                                    

EXAMPLE 18

Ten grams of defatted soybean flour and 5 g. Supro-7 were mixed in 30ml. water at room temperature. The mixture was frozen and freeze dried.The dried product had a needle-like texture resembling muscle fibers. Itwas heat cured at 185° C. for 30 minutes to give a non-water dispersibleproduct. This product was sponge-like and it absorbed water. The wetproduct had a meat-like handfeel and was chewable.

Examples 19-25 illustrate one aspect of the process of this inventionwherein the heat treatment is carried out by autoclaving in alcohol.

EXAMPLE 19

Torula yeast (Candida utilis) was grown in a fermentor on an ethanol andminerals medium. The cells were harvested by centrifugation and thepaste (about 20% dry weight) was mixed with Supro-7 at room temperatureto obtain a yeast paste to Supro-7 ratio of about 2/1. Water was addedto obtain slurries or pastes of 15 to 40% dry weight. The mixtures werefrozen and freeze dried. The freeze dried products were dispersible inwater, but retained their rigid texture when dipped in 96% ethanol. Whenremoved from ethanol, air dried and dipped in water, they dispersed.Dispersion in water was eliminated by autoclaving the ethanol soakedproducts for 15 to 120 minutes under about 15 psig. pressure at about121° C. The autoclaved product was either dried in air or in an oven at50° C. The dry product had a texture composed of needle-like filaments.It was chewable without dispersion in the mouth. When dipped in water,it remained intact and swelled by absorption of water. The water couldbe squeezed out of the product and reabsorbed without significant changein textural integrity of the product.

EXAMPLE 20

The autoclaved product obtained in Example 19 was dried and further heattreated at 150° C. in a dry air oven. The product was white in color. Itretained its textural characteristics in water.

EXAMPLE 21

The procedure of Example 19 was repeated, except that instead ofautoclaving the freeze dried product in ethanol, it was autoclaved inisopropanol. A white product which retained its texture in water wasobtained.

EXAMPLE 22

The procedure of Example 19 was repeated, except that instead ofautoclaving in ethanol, the freeze dried product was autoclaved directlyeither in an open beaker or in a sealed vial. Both autoclaved productslost their texture when placed in water.

EXAMPLE 23

The procedure of Example 19 was repeated, except that instead of 96%ethanol, 20%, 40%, 60%, 75%, 80%, 85%, and 90% ethanol solutions inwater were used during autoclaving. In all cases the final productresisted dispersion in water. When solutions with less than 60% ethanolcontent were used, however, the solutions had to be added gently orotherwise the textural integrity of the products was lost prior toautoclaving.

EXAMPLE 24

A slurry was prepared with 2 g. of ethanol-extracted, spray dried Torulayeast, 1 g. Supro-7, and 9 ml. distilled water. The mixture was frozenand freeze dried. The freeze dried product was dipped in 90% ethanol andautoclaved for 30 minutes at about 121° C. under about 15 psig. pressurein a sealed tube. The autoclaved product was taken out of the ethanoland dried in an oven at 80° C. The dry product was white in color andhad a chicken meatlike appearance. When soaked in water, the productabsorbed water but did not disperse.

EXAMPLE 25

A slurry was prepared with 2 g. of defatted soybean flour, 1 g. Supro-7,and 9 ml. distilled water. The mixture was frozen and freeze dried. Thedry product was dipped in ethanol and autoclaved for 1 hour at about121° C. and about 15 psig. The ethanol was then decanted out and theresidue was dried at 50° C. in a hot air oven. The final productretained its textural integrity in water.

Examples 26-27 serve to illustrate one aspect of the process of thisinvention incorporating the use of cold alcohol as a replacement forfreeze drying to dehydrate the frozen mixture.

EXAMPLE 26

A slurry was prepared by using 2 g. Torula yeast (ethanol extracted andoven dried), 1 g. Supro-7, and 9 ml. water. The slurry was frozen overdry ice. The frozen mass was broken into pieces measuring about1/2"×1/4"×1" and soaked in about -10° C. cold ethanol for about threehours. After three hours the mixture was heated for about 45 minutes insealed tubes at about 121° C. under about 15 psig pressure. The heattreated pieces remained intact in the autoclave. The excess liquid wasdecanted off and the pieces were dried in an oven at 50° C. The dryproducts did not disperse in water. The wet products had a sponge-liketexture and became swollen as they absorbed water. The dry and wetproducts were white to light gray in color and had a neutral taste.

EXAMPLE 27

The ethanol soaked product obtained in Example 26 was put in an oven at100° C. to dry and then further heat treated at about 190° C. to renderit non-water dispersible.

It will be clear to those skilled in the art that many variations can bemade from these examples, shown for purposes of illustration, withoutdeparting from the scope of this invention.

We claim:
 1. A process for texturizing an aqueous slurry of single-cellprotein materials comprising:(a) adding to the aqueous slurry ofsingle-cell protein materials a texturizing agent selected from thegroup consisting of protein isolates, protein concentrates, gelatin, ormixtures thereof, wherein the dry weight ratio of the single-cellprotein material to the texturizing agent is in the range of from about1:9 to about 9:1; (b) heating the aqueous slurry to a temperature offrom about 30° to about 130° C.; (c) whipping the heated slurry to forma foam; (d) freezing the foam; (e) dehydrating the frozen foam; and (f)heat treating the dehydrated foam at a temperature of from about 130° toabout 230° C. for from about 3 to about 120 minutes to yield awater-stable textured product.
 2. The process of claim 1 wherein thetextured product is ethanol-extracted to improve its flavorcharacteristics.
 3. The process of claim 1 wherein the frozen foam isoven dried at a temperature of from about 50° to about 200° C.
 4. Theprocess of claim 1 wherein the frozen foam is microwave dried.
 5. Theprocess of claim 1 wherein the frozen foam is freeze dried.
 6. Theprocess of claim 1 wherein the texturizing agent is soy isolate.
 7. Theprocess of claim 1 wherein the texturizing agent is a mixture of soyisolate and gelatin.
 8. The process of claim 1 wherein the single-cellmaterial is Candida utilis yeast.
 9. The product prepared by the processof claim 1.